Salmonella strains TA1535, TA1537, TA1538, TA98, TA100, TA97 and TA102 are being used to test chemicals of interest for mutagenicity. Diethylstilbestrol (DES) will be tested for mutagenicity in strain TA102 using various metabolic activation systems. Some antioxidants which have been shown to cause mutagenic suppression in TA100 will be looked at in other strains as well. Pyrene, which has so far been shown to have inconsistent mutagenic results and which is considered an inactive analog of the carcinogenic benzy(a)pyrene, is being studied with the new Ames' tester strain, TA97. Also, the mutagenicity data for ethylnitrosourea is incomplete, so this chemical will be studied using a number of Salmonella tester strains.